RE: Re: Fourier frequencies
- To: mathgroup at smc.vnet.net
- Subject: [mg43524] RE: [mg43428] Re: [mg43401] Fourier frequencies
- From: "kimsj" <kimsj at mobile.snu.ac.kr>
- Date: Fri, 19 Sep 2003 03:41:48 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
> -----Original Message----- > From: Sseziwa Mukasa [mailto:mukasa at jeol.com] To: mathgroup at smc.vnet.net > Sent: Wednesday, September 17, 2003 8:59 PM > To: mathgroup at smc.vnet.net > Subject: [mg43524] [mg43428] Re: [mg43401] Fourier frequencies > > > On Friday, August 29, 2003, at 07:16 AM, akpovo wrote: > > > Hello to all, > > How possible is it to compute a fourier transform of a data set {t,x} > > in > > order to have the fourier coefficient and the corresponding frequency? > > Tahnks > > > > > > The Fourier Transform is computed as normal > > Fourier[x] > > Traditionally the 0 frequency is placed in the center of the spectrum, > after an FFT though it is at the left so we rotate the data: > > RotateRight[Fourier[x],Quotient[Length[x],2] > > The frequencies are determined from the time with the following function > > freq[t_]:=With[{tau=t[[2]]-t[[1]],n=Length[t]},Table[-tau/2+i/(n > tau),{i,0,n-1}] > > You can the use ListPlot to get the spectrum, assuming the data is in > the list x and the times in the list t > > ListPlot[Transpose[{freq[t],RotateRight[Fourier[x],Quotient[Length[x],2] > ]}],PlotJoined->True] > > Regards, > > Ssezi Akpovo, If you want to do symbolic Fourier transform sometimes besides discrete Fourier transform, you may use the function FourierTransform[] on the contrast to Fourier[]. -- Regards, --- James (txdiversity at hotmail.com) - Private opinions: These are not the opinions from my affiliation.